Most folding knives incorporate some kind of a mechanism that holds the blade or working implement in the closed position in which the sharp edge of the blade is held safely within the handle. There are many known mechanisms for retaining blades in the closed position, and there are obvious reasons why such mechanisms are used. Among other reasons, blade-retaining mechanisms prevent unintended opening of the knife and thus promote safety.
Automatic opening mechanisms and so-called “opening assist” mechanisms may be incorporated into folding knives. Generally speaking, in a knife that has an automatic opening mechanism the blade is held in the closed position by a latched trigger mechanism. When closed, the blade is under a constant “pre-load” pressure from a spring mechanism. When the trigger is released, the blade is automatically driven by the spring mechanism into the open position. On the other hand, with knives that incorporate opening assist mechanisms the blade is retained in the closed position without the need for a latch or trigger. The opening assist function is provided by a spring mechanism that operates on the blade. As the user manually rotates the blade from closed toward the open position, the spring mechanism that acts on the blade reaches a threshold point. After the blade rotates beyond the threshold point the spring drives the blade to the open position.
Both knives equipped with automatic and opening assist mechanisms typically include some kind of locking mechanism to lock the blade open, and with many opening assist knives the same spring mechanism that drives the blade open also retains the blade closed.
For a variety of reasons, opening assist mechanisms are becoming very popular. For example, in appropriate circumstances and for appropriate users, there are many advantages to be derived from assisted opening knives and many situations where automatic knives can be useful. These often include situations where the user has only one hand free. However, even in a knife that includes an automated opening or opening assist mechanism, safety considerations always mandate that the blade stays in the closed position until the user volitionally and intentionally moves the blade into the open position. For example, a mechanism that holds a knife blade closed should never release when the knife is dropped. With the recent increases in popularity of opening assist knives there are many new types of mechanisms being developed.
There is always a need however for mechanisms that provide an opening assist feature for knives.
The present invention comprises folding knife having an opening assist mechanism. In a first illustrated embodiment, the mechanism of the present invention relies upon a pair of torsion springs held axially on the blade axis pin and within a pair of bushings that are stationary relative to the knife handle. There is one spring and one bushing on each lateral side of the blade. One leg of each spring is fixed to the bushing. The opposite leg of the spring rides in a pocket formed in the surface of the blade axially around the opening through which the blade axis pin is inserted. When the blade is in the closed position the torsion springs are “loaded” but do not apply their spring force to the blade, instead applying their force against the stationary bushing. As the blade rotates from the closed position toward the open position, the legs of the springs rotate through and cooperate with structures formed on the bushings to transfer the spring pressure instantly from the bushing to the blade to drive the blade open. As the blade is thus rotated from the closed position toward the open position, once a predetermined rotational point, or “threshold” point in the rotational movement of the blade is passed, the mechanism of the present invention rotationally drives the blade into the fully open position. This is accomplished with the paired springs, which act on the blade and thereby impart sufficient rotational kinetic energy to the blade that the inertia drives the blade into the fully open position. A locking mechanism locks the blade in the open position. As the blade is rotated from the open position to the closed position the torsion springs are once again loaded, and once a desired rotational point is passed one leg of each of the spring moves into a pocket in the bushing and the spring's rotational force is transferred from the blade to the stationary bushing, allowing the blade to remain in the closed position.
The mechanism of the present invention may also be built to rely upon only one torsion spring, which is structurally and functionally identical to the paired springs described above.